Art is essentially the physical expression of ANY concept...
Art has many purposes
Art is essentially the physical expression of ANY concept or idea- be it beauty, death etc. Some of the most powerful works of art would not be considered beautiful- for example the work of Francis Bacon- but are held in high regard because of the ability of the artist to convey a sense of something. While many works of art convey a sense of beauty, it is certainly not the only purpose of art as a whole.